Oil, gas and geothermal wells typically require that at least two strings of pipe, at least one of which is a casing string, be hung from a single support member, such as a wellhead member, and this is conventionally accomplished by securing a pipe hanger to the last joint of the string and landing the hanger in the support member. In some cases, the hanger for the outermost string is landed on a shoulder in the through bore of the support member and the hangers for the remaining strings are supported in series by the first-landed hanger, as seen for example in U.S. Pat. Nos. 3,268,243 issued Aug. 23, 1966, to W. W. Word, and 3,105,552, issued Oct. 1, 1963, to J. A. Haeber et al. While such practices are satisfactory for relatively shallow wells, they are not truly suitable for very deep wells where the loads applied by the pipe strings are so large that it is not desirable to support the aggregate load of all of the strings on a single shoulder. Some prior-art workers have therefore provided wellheads in which the through bore has one shoulder for each pipe hanger, the bore therefore being of stepped diameter as seen, for example, in U.S. Pat. No. 3,084,745, issued Apr. 9, 1963, to J. F. Floyd. Particularly for deep underwater wells, that practice is frequently not acceptable because the annular space available is not adequate to allow a stepped diameter through bore in the wellhead or like support member. Accordingly, there has been a continuing need for a method and apparatus which would make it practical to install each of several pipe hangers on its own support within the through bore of a wellhead body or like support member when the through bore is of constant diameter, in such fashion that each hanger transfers the load of its pipe string directly to the support member with substantially none of the load being transferred to the subadjacent pipe hanger.
In earlier times, when the weights of pipe strings were far less than today and when wells were established on land, so that the wellhead was immediately available to the human operators, prior-art workers proposed having each pipe hanger supported independently on the wellhead body by equipping the hanger with outwardly urged segments or dogs, the hanger simply being lowered until the segments or dogs reached a desired groove, whereupon the segments or dogs snapped outwardly to engage in that groove, with the hanger then being supported on the lower wall of the groove, as shown for example in U.S. Pat. No. 2,035,834, issued Mar. 31, 1936, to A. J. Penick et al. Though such approaches were practical for installations in which the wellhead or other support member was available to view and for direct manipulation of the equipment, they were not adopted for underwater installations in which the load of the pipe string was very large and the annular space available in the support member was small. For such applications, prior-art workers went to relatively complex structures such as those seen in U.S. Pat. Nos. 3,086,590, issued Apr. 23, 1963, to J. G. Jackson et al; 3,090,438, issued May 21, 1963, to G. M. Raulins; and 3,099,317, issued July 30, 1963, to W. L. Todd. There has accordingly been a continuing need for simplification and improvement of such pipe hanging methods and apparatus.